When mine start molting, I add just a little dry cat kibble to their diet. The idea is that it boosts the protein that is needed to make feathers. I try not to overdo it, though.

If it has been a while - and I feel that a year is a while - since molting, the feathers can start to look a little rough. I remember one year Vier was copper-colored, rather than her walnut-brown color. She finally molted and restored the rich browns, but also started developing white feathers (snow). Hazel was pearl white when we adopted her, then she molted back to her buff color.